共查询到20条相似文献,搜索用时 250 毫秒
1.
提出了一种制备单分散M型钡铁氧体空心球的新方法,即以碳酸胍表面改性的单分散聚(苯乙烯-共-丙烯酸)P(St-co-AA)乳胶粒子为模板,在其表面原位诱导钡铁氧体前驱物的定位并生长,以此获得壳层均匀致密的P(St-co-AA)/钡铁氧体前驱物核壳复合粒子,再经过热处理得到结构完整、成分单一的M型钡铁氧体空心球. 相似文献
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采用水热法,利用乙醇和水的混合溶剂合成了单分散钛酸锶纳米晶体。X射线衍射(XRD)结果显示该晶体为立方相,延长反应时间其结晶性增强。扫描电子显微镜(SEM)、透射电子显微镜(TEM)结果显示样品为70nm左右的均匀立方块晶体。利用SEM、TEM、高分辨透射电子显微镜(HRTEM)和电子衍射(ED)谱研究了该纳米晶体的生长过程,结果表明:前驱体经过扩散反应生成钛酸锶晶核,晶核之间由于定向生长作用而团聚连接形成颗粒球,最后颗粒球在缓慢的奥斯特瓦尔德熟化作用下转化为钛酸锶晶体。这一“扩散反应、定向生长、奥斯特瓦尔德熟化”的生长过程揭示了钛酸锶纳米晶体的生长机理。利用Johnson-Mehl-Avrami(JMA)方程模拟证实了其初始阶段的扩散反应机理,并得出反应活化能为15.79kJ·mol-1。 相似文献
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采用水热法,利用乙醇和水的混合溶剂合成了单分散钛酸锶纳米晶体.X射线衍射(XRD)结果显示该晶体为立方相,延长反应时间其结晶性增强.扫描电子显微镜(SEM)、透射电子显微镜(TEM)结果显示样品为70 nm左右的均匀立方块晶体.利用SEM、TEM、高分辨透射电子显微镜(HRTEM)和电子衍射(ED)谱研究了该纳米晶体的生长过程,结果表明:前驱体经过扩散反应生成钛酸锶晶核,晶核之间由于定向生长作用而团聚连接形成颗粒球,最后颗粒球在缓慢的奥斯特瓦尔德熟化作用下转化为钛酸锶晶体.这一“扩散反应定向生长奥斯特瓦尔德熟化”的生长过程揭示了钛酸锶纳米晶体的生长机理.利用Johnson-Mehl-Avrami(JMA)方程模拟证实了其初始阶段的扩散反应机理,并得出反应活化能为15.79 kJ·mol-1. 相似文献
4.
通过水热合成法制备了单分散碳微球, 并以此单分散碳微球为核, 利用其表面修饰的银纳米粒子作为种子, 进一步还原制备了以碳微球为核、以金为壳的金纳米壳(Nanoshell)球体. 通过透射电子显微镜和紫外可见吸收光谱对其形态以及光谱性质进行了表征. 研究结果表明, 采用该种方法制备出来的碳微球具有良好的单分散性, 表面修饰简便快捷, 利用碳微球为核制备的金纳米壳球体尺寸可控, 在近红外范围内有强吸收. 实验结果证明该方法是制备金纳米壳球体的一种有效新方法. 相似文献
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Lynch J Zhuang J Wang T LaMontagne D Wu H Cao YC 《Journal of the American Chemical Society》2011,133(32):12664-12674
This paper reports that gas bubbles can be used to tailor the kinetics of the nucleation and growth of inorganic-nanocrystals in a colloidal synthesis. We conducted a mechanistic study of the synthesis of colloidal iron oxide nanocrystals using gas bubbles generated by boiling solvents or artificial Ar bubbling. We identified that bubbling effects take place through absorbing local latent heat released from the exothermic reactions involved in the nucleation and growth of iron oxide nanocrystals. Our results show that gas bubbles display a stronger effect on the nucleation of iron oxide nanocrystals than on their growth. These results indicate that the nucleation and growth of iron oxide nanocrystals may rely on different types of chemical reactions between the iron-oleate decomposition products: the nucleation relies on the strongly exothermic, multiple-bond formation reactions, whereas the growth of iron oxide nanocrystals may primarily depend upon single-bond formation reactions. The identification of exothermic reactions is further consistent with our results in the synthesis of iron oxide nanocrystals with boiling solvents at reaction temperatures ranging from 290 to 365 °C, by which we determined the reaction enthalpy in the nucleation of iron oxide nanocrystals to be -142 ± 12 kJ/mol. Moreover, our results suggest that a prerequisite for effectively suppressing secondary nucleation in a colloidal synthesis is that the primary nucleation must produce a critical amount of nuclei, and this finding is important for a priori design of colloidal synthesis of monodispersed nanocrystals in general. 相似文献
12.
Shevchenko EV Talapin DV Schnablegger H Kornowski A Festin O Svedlindh P Haase M Weller H 《Journal of the American Chemical Society》2003,125(30):9090-9101
High quality CoPt(3) nanocrystals were synthesized via simultaneous reduction of platinum acetylacetonate and thermodecomposition of cobalt carbonyl in the presence of 1-adamantanecarboxylic acid and hexadecylamine as stabilizing agents. The high flexibility and reproducibility of the synthesis allows us to consider CoPt(3) nanocrystals as a model system for the hot organometallic synthesis of metal nanoparticles. Different experimental conditions (reaction temperature, concentration of stabilizing agents, ratio between cobalt and platinum precursors, etc.) have been investigated to reveal the processes governing the formation of the metal alloy nanocrystals. It was found that CoPt(3) nanocrystals nucleate and grow up to their final size at an early stage of the synthesis with no Ostwald ripening observed upon further heating. In this case, the nanocrystal size can be controlled only via proper balance between the rates for nucleation and for growth from the molecular precursors. Thus, the size of CoPt(3) nanocrystals can be precisely tuned from approximately 3 nm up to approximately 18 nm in a predictable and reproducible way. The mechanism of homogeneous nucleation, evolution of the nanocrystal ensemble in the absence of Ostwald ripening, nanocrystal faceting, and size-dependent magnetic properties are investigated and discussed on the example of CoPt(3) magnetic alloy nanocrystals. The developed approach was found to be applicable to other systems, e.g., FePt and CoPd(2) magnetic alloy nanocrystals. 相似文献
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Kwon SG Piao Y Park J Angappane S Jo Y Hwang NM Park JG Hyeon T 《Journal of the American Chemical Society》2007,129(41):12571-12584
We studied the kinetics of the formation of iron oxide nanocrystals obtained from the solution-phase thermal decomposition of iron-oleate complex via the "heating-up" process. To obtain detailed information on the thermal decomposition process and the formation of iron oxide nanocrystals in the solution, we performed a thermogravimetric-mass spectrometric analysis (TG-MS) and in-situ magnetic measurements using SQUID. The TG-MS results showed that iron-oleate complex was decomposed at around 320 degrees C. The in-situ SQUID data revealed that the thermal decomposition of iron-oleate complex generates intermediate species, which seem to act as monomers for the iron oxide nanocrystals. Extensive studies on the nucleation and growth process using size exclusion chromatography, the crystallization yield data, and TEM showed that the sudden increase in the number concentration of the nanocrystals (burst of nucleation) is followed by the rapid narrowing of the size distribution (size focusing). We constructed a theoretical model to describe the "heating-up" process and performed a numerical simulation. The simulation results matched well with the experimental data, and furthermore they are well fitted to the well-known LaMer model that is characterized by the burst of nucleation and the separation of nucleation and growth under continuous monomer supply condition. Through this theoretical work, we showed that the "heating-up" and "hot injection" processes could be understood within the same theoretical framework in which they share the characteristics of nucleation and growth stages. 相似文献
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Synthesis of monodisperse spherical nanocrystals 总被引:2,自引:0,他引:2
Park J Joo J Kwon SG Jang Y Hyeon T 《Angewandte Chemie (International ed. in English)》2007,46(25):4630-4660
Much progress has been made over the past ten years on the synthesis of monodisperse spherical nanocrystals. Mechanistic studies have shown that monodisperse nanocrystals are produced when the burst of nucleation that enables separation of the nucleation and growth processes is combined with the subsequent diffusion-controlled growth process through which the crystal size is determined. Several chemical methods have been used to synthesize uniform nanocrystals of metals, metal oxides, and metal chalcogenides. Monodisperse nanocrystals of CdSe, Co, and other materials have been generated in surfactant solution by nucleation induced at high temperature, and subsequent aging and size selection. Monodisperse nanocrystals of many metals and metal oxides, including magnetic ferrites, have been synthesized directly by thermal decomposition of metal-surfactant complexes prepared from the metal precursors and surfactants. Nonhydrolytic sol-gel reactions have been used to synthesize various transition-metal-oxide nanocrystals. Monodisperse gold nanocrystals have been obtained from polydisperse samples by digestive-ripening processes. Uniform-sized nanocrystals of gold, silver, platinum, and palladium have been synthesized by polyol processes in which metal salts are reduced by alcohols in the presence of appropriate surfactants. 相似文献
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This review highlights work from the authors’ laboratory on the recent development of seed-mediated growth method for noble metal nanocrystals. The seed-mediated growth method has become one of the most efficient and versatile methods for synthe-sizing high-quality noble metal nanocrystals. The seed-mediated growth method can separate the nucleation and growth stages of metal nanocrystals, and thus provide better control over the size, size distribution, and crystallographic evolution of metal nanocrystals. Because of its high controllability, the seed-mediated growth method is especially promising in providing mechanistic insights into the growth mechanisms of noble metal nanocrystals. In this review, the thermodynamic and kinetic parameters for the nucleation and growth of noble metal nanocrystals are systematically summarized. Mechanistic understanding of these parameters is provided. These studies provide useful guidelines for the rational design and synthesis of novel noble metal nanocrystals with high quality. 相似文献
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Wang DS Xie T Peng Q Zhang SY Chen J Li YD 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(8):2507-2513
We have developed a method for the synthesis of metal oxide nanocrystals with controllable shape and size, which is based on the direct thermal decomposition of metal nitrates in octadecylamine. Mn3O4 nanoparticles and nanorods with different lengths were synthesized by using manganese nitrate as the decomposition material. Other metal oxide nanocrystals such as NiO, ZnO, CeO2, CoO, and Co3O4 were also prepared by this method. These nanocrystals were then assembled into 3D colloidal spheres by a surfactant-assisted self-assembly process. Subsequently, calcination was carried out to remove the surfactants to obtain mesoporous metal oxides, which show large pores, good crystallization, thermally stable pore mesostructures, and potential applications in various fields, especially in catalysis and lithium-ion batteries. 相似文献
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In the present study, metal nanocrystals were obtained by the very easy, economical, and nontoxic thermal decomposition method and stabilized by coating oleate without any solvent. These nanocrystals have a highly crystalline structure due to a high decomposition temperature (~563-573 K) at low pressure and very narrow distribution. The prepared Fe3O4 nanocrystals were controlled by the annealing time and vacuum pressure. A TEM image of monodispersed Fe3O4 nanocrystals showed the 2D assembly of nanocrystals, demonstrating their uniformity. The particle size is 10.6 +/- 1.2 nm. TEM images of silver nanocrystals a showed 2D assembly with 9.5 +/- 0.7 nm. An electron diffraction image and X-ray diffraction of the nanocrystals showed the highly crystalline nature of metal nanocrystals. 相似文献
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The mechanisms responsible for the formation of the shell in core-shell nanocrystals are ion-displacement and heterogeneous nucleation. In the ion-displacement mechanism, the shell is formed by the displacement reaction at the surface of the core nanoparticle whereas in heterogeneous nucleation the core particle induces the nucleation (or direct deposition) of shell material on its surface. The formation of core-shell nanocrystals via the post-core route has been examined in the current investigation. A purely probabilistic Monte Carlo scheme for the formation of the shell has been developed to predict the experimental results of Hota et al. (Hota, G.; Jain, S.; Khilar, K. C. Colloids Surf., A 2004, 232, 119) for the precipitation of Ag2S-coated CdS (Ag2S@CdS) nanoparticles. The simulation procedure involves two stages. In the first stage, shell formation takes place as a result of the consumption of supersaturation, ion displacement, and reaction between Ag+ and excess sulfide ions. The growth in the second stage is driven by the coagulation of nanoparticles. The results indicate that the fraction of shell deposited by the ion-displacement mechanism increases with increasing ion ratio and decreases with increasing water-to-surfactant molar ratio. 相似文献
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The sulfidation of colloidal rock-salt-type MO (M = Fe, Mn and Co) nanocrystals was performed in organic solvents using dissolved elemental sulfur at moderate temperatures. The vacancy defects in these rock-salt-type structures clearly promote complete oxide-sulfide conversion. The conversion products were hollow metal sulfide (pyrrhotite (Fe(1-x)S), Co(1-x)S and α-MnS) nanoparticles. These conversions by sulfidation proceed rapidly, making difficult the isolation of intermediates. The sulfidation intermediates, when the supply of sulfur was insufficient, had interesting structures, in which the metal oxide cores were surrounded by metal sulfide shells or had surfaces that were decorated with metal sulfide islands. Based on the above results, a mechanism of surface nucleation, shell formation, and void formation by diffusion processes is proposed. 相似文献
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Herring NP AbouZeid K Mohamed MB Pinsk J El-Shall MS 《Langmuir : the ACS journal of surfaces and colloids》2011,27(24):15146-15154
This work reports the development of a fast and simple "one-pot" route for the synthesis of hybrid Au-ZnO hexagonal nanopyramids by sequential homogeneous-heterogeneous nucleation steps involving both Au and Zn ions using microwave irradiation (MWI). The rapid decomposition of zinc acetate by MWI in the presence of a mixture of oleic acid (OAc) and oleylamine (OAm) results in the formation of hexagonal ZnO nanopyramids. In the presence of Au ions, the initially formed Au nanocrystals act as heterogeneous nuclei for the nucleation and growth of the ZnO nanopyramids. The Au nanoparticles promote the heterogeneous nucleation of ZnO and the formation of the hexagonal base of the ZnO nanopyramids. Using preformed Au nanoparticles instead of Au ions results in a narrow size distribution of uniform Au-ZnO nanopyramids, each consisting of a gold nanoparticle embedded in the center of the hexagonal base of the ZnO nanopyramid. We study the factors that control the nucleation and growth of these complex structures, and provide new insights into the stepwise homogeneous-heterogeneous mechanism and the conventional heterogeneous nucleation on preformed Au nanoparticles. The formation of the hetero nanostructures Au-ZnO nanopyramids is strongly dependent on the molar ratios of OAc to OAm. The presence of OAc with a considerable dipole moment results in strong electrostatic interaction with the polar surfaces of the growing ZnO nanocrystals thus resulting in slowing the growth rate of the polar planes and allowing the formation of well-developed facets. In the absence of Au nanoparticles, a high concentration of zinc acetate and longer MWI times are required for the production of the nanopyramids. The gold nanoparticles could provide the metallic contact points within the hybrid nanopyramids which could facilitate the bottom-up assembly of Au-ZnO devices. Furthermore, the Au-ZnO nanopyramids could have improved performance in solar energy conversion and photocatalysis. 相似文献